1. Field of the Invention
The present invention relates to MEMS (Micro Electro Mechanical System) transducers applied to MEMS sensors used in miniature condenser microphones, vibration sensors, pressure sensors, and acceleration sensors, for example.
The present invention also relates to manufacturing methods of MEMS transducers.
The present application claims priority on Japanese Patent Application No. 2007-341440, and Japanese Patent Application No. 2007-341426, the contents of which are incorporated herein by reference.
2. Description of the Related Art
Various types of miniature condenser microphones, which are manufactured by use of manufacturing processes of semiconductor devices, have been developed and disclosed in various documents such as Patent Documents 1, 2, 3, and Non-Patent Document 1.                Patent Document 1: Japanese Patent Application Publication No. H09-50877        Patent Document 2: Japanese Patent Application Publication No. 2004-506394        Patent Document 3: U.S. Pat. No. 4,776,019        Non-Patent Document 1: MSS-01-34 published by Japanese Institute of Electrical Engineers        
Condenser microphones have been referred to as MEMS microphones, each of which is designed such that a diaphragm and a plate (which are formed using thin films so as to form opposite electrodes of a parallel-plate condenser) are separated from each other and are supported above a substrate. When the diaphragm vibrates due to sound waves, the displacement thereof occurs so as to vary electrostatic capacitance of the condenser, so that variations of electrostatic capacitance are converted into electric signals. MEMS transducers serving as condenser microphones are covered with protective films on the surfaces thereof, wherein through-holes are formed in protective films so as to expose electrodes. The protective films having insulating properties are used to protect MEMS transducers from chemical corrosions (due to water, oxygen, and sodium) and physical damages.
Relatively high stresses occur on deposited films composed of nitride materials and nitrogen oxide materials which are deposited on silicon substrates and silicon oxide films due to differences in thermal expansion coefficients. When nitride materials and nitrogen oxide materials are used for protective films, distortions may occur in MEMS transducers having mechanical structures. This may damage the mechanical functions of MEMS transducers.